make button inactive when submitted

rowers/templates/braintreedropin.html

@@ -23,3 +23,12 @@
     });
   });
 </script>
+<script type='text/javascript'
+        src='https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js'>
+</script>
+<script>
+$('#payment-form').submit(function() {  
+$(this).find("button[type='submit']").prop('disabled',true);
+console.log("disabled");
+}
+</script>

rowers/templates/upgradeconfirm.html

@@ -91,7 +91,12 @@
         cycle, you will be charged for a prorated amount. For example, when
         you upgrade from a 15€ plan to a 65€ plan (a difference of
         50€) in the 6th month of the 12 month billing cycle, you
-        will be charged 35€.
+        will be charged 25€.
+      </p>
+      <p>
+        After you hit the Upgrade button, the transaction will be launched.
+        Please wait until the transaction completes. Do not click the
+        button twice. Do not close your browser window.
       </p>
   </li>
 </ul>